Molding is a process by virtue of which a molded article can be formed from molding material by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. One example of the molded article that can be formed, for example, from polyethylene terephthalate (PET) material is a preform that is capable of being subsequently blow-molded into a beverage container, such as, a bottle and the like. Other examples of the molded articles include thin-wall containers (i.e. yogurt containers, cups, etc), medical appliances and the like.
In the early days of injection molding, a single-cavity mold for producing a single molded article per molding cycle was typically deployed. Within the single-cavity mold, typically, melt would be delivered from a plasticizing unit to a molding cavity, defined within the single-cavity mold, via a sprue. With developments in the injection molding art, multi-cavity molds have been introduced with an outlook to increase the number of molded articles manufactured per molding cycle. Typically, within the multi-cavity mold, the melt is delivered from the plasticizing unit to each of a plurality of molding cavities of the multi-cavity mold through a melt distribution network, also known to those of skill in the art, as a “hot runner”.
With ongoing market pressures on the converters (i.e. entities that convert raw material, such as resin, into a molded article, such as a preform, for example) to keep the output per capita and the operating costs under control (and, even better, to improve the output per capita ratio and decrease the costs), molding machine suppliers (such as, for example, Husky Injection Molding, Ltd of Bolton, Ontario, www.husky.ca) have progressively increased mold cavitation, effectively, increasing the number of molded articles that can be produced in a given molding cycle.
With further increases in cavitation, a term “tight pitch” has become widely used. The term denotes a mold having a relatively tight pitch between cavities. For example, Husky Injection Molding Systems, Ltd sells such molds under a trademark MICROPITCH. One problem that has been realized in the industry, which is particularly acute in the tight pitch molds, is irregular distribution of forces amongst various components of the mold in the mold clamped configuration. This is particularly exacerbated by the fact that even though mold stack components are produced to very tight tolerances, there are nevertheless minute differences in dimensions (such as for example, height thereof) that may significantly exacerbate the problem. This problem can be further exacerbated by lack of proper platen parallelism, platen deflection in use and the like.
Consider a given mold having 144 cavities and, accordingly, 144 mold stacks (including a molding cavity insert, a core insert, a neck ring pair and other associated molding components). A first given one of the 144 mold stacks may be slightly higher than a second given one of the 144 mold stacks. In this scenario, when full clamp force is exerted onto the mold, the first given one of the 144 mold stacks will experience deformation. This, in turn, can lead to premature wear, molding defects evident on molded articles and the like.
By adding more cavities into a mold, the available shut-off area is limited and usually falls below a given standard. This, in turn, requires adding shut-off area with external features. One solution pursued in the industry has been introduction of so-called “tonnage blocks”, which are primarily (but not exclusively) used on tight pitch molds. Generally speaking, the reason to add tonnage blocks to a mold is to increase the surface area in contact under clamp in order to prevent permanent deformation of the shut-off faces (also known as hobbing). The tonnage block generally comprises a structure inserted in-between complementary mold halves and is generally configured to absorb or re-distribute at least a portion of the clamp force.
US patent application 2007/0212443 published to Guoming, et al. on Sep. 13, 2007 discloses an injection mold including a connecting structure for separating confronting faces of a slide member and a mold base, respectively, during a movement of the slide member. In accordance with several embodiments of the invention, the connecting structure may include a compressible member such that the slide member is biased away from the mold base, and wherein a positive contact between the confronting surfaces is configurable in response to an applied clamping force between the slide member and the mold base. In accordance with an alternative embodiment of the invention a cam arrangement links the slide member and the mold base enabling a positive contact between the confronting surfaces when the slide member is arranged in the in-mold position, and providing a gap between the confronting surfaces during at least a portion of an interval when the slide member is moving. The patent application teaches inter alia a clamping force block 29, which is added (if necessary) to absorb clamping force A (FIG. 1), which goes through the mold stack when such clamping force is too high.
US patent application 2007/0292558 published to Irwine et al. on Dec. 20, 2007 discloses a hot-runner assembly for injection molding equipment. The hot-runner assembly includes a front plate and a backing plate spaced from one another so as to define an inter-plate volume. The inter-plate volume contains one or more manifolds for conducting flowable material to a plurality of injection nozzles. The inter-plate volume also contains inter-plate support distributed between a first inter-plate support zone located immediately adjacent the manifold(s) and a second inter-plate support zone that makes up the balance of the inter-plate volume so that the first inter-plate support zone has a inter-plate support footprint density that is greater than the inter-plate support footprint density in the second inter-plate support zone. This patent application teaches inter alia an inter-plate support 120.
US patent application 2007/0184148 published to Naoto, et al. on Aug. 9, 2007 discloses a mold for in-mold decorating simultaneously with molding manufacturable at low cost in a short delivery period in manufacturing the mold and capable of stably mass-producing molded article in molding the molded articles, wherein cavity forming blocks having molding cavities into which an in-mold decoration film is to be inserted are mounted on diesets on a fixed side and a movable side. Pockets into which the cavity forming blocks are fitted are not formed in the diesets, the diesets and cavity forming blocks are positioned by engaging projections formed on one of the contact faces thereof and engaging recesses formed in the other before installation, and a plurality of mold clamping force receiving parts are installed on the outside of a film passing area around the cavity forming blocks. This patent application teaches inter alia a plurality of clamping force-receiving portions 6a, 6b that are set partly around the cavity-forming blocks.